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  <div class="question_difficulty">
   难度：Easy
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   <h1 class="question_title">
    326. Power of Three
   </h1>
   <p>
    Given an integer, write a function to determine if it is a power of three.
   </p>
   <p>
    <b>
     Example 1:
    </b>
   </p>
   <pre>
<strong>Input:</strong> 27
<strong>Output:</strong> true
</pre>
   <p>
    <b>
     Example 2:
    </b>
   </p>
   <pre>
<strong>Input:</strong> 0
<strong>Output:</strong> false</pre>
   <p>
    <b>
     Example 3:
    </b>
   </p>
   <pre>
<strong>Input:</strong> 9
<strong>Output:</strong> true</pre>
   <p>
    <b>
     Example 4:
    </b>
   </p>
   <pre>
<strong>Input:</strong> 45
<strong>Output:</strong> false</pre>
   <p>
    <b>
     Follow up:
    </b>
    <br>
    Could you do it without using any loop / recursion?
   </p>
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   <h1 class="question_title">
    326. 3的幂
   </h1>
   <p>
    给定一个整数，写一个函数来判断它是否是 3&nbsp;的幂次方。
   </p>
   <p>
    <strong>
     示例 1:
    </strong>
   </p>
   <pre><strong>输入:</strong> 27
<strong>输出:</strong> true
</pre>
   <p>
    <strong>
     示例 2:
    </strong>
   </p>
   <pre><strong>输入:</strong> 0
<strong>输出:</strong> false</pre>
   <p>
    <strong>
     示例 3:
    </strong>
   </p>
   <pre><strong>输入:</strong> 9
<strong>输出:</strong> true</pre>
   <p>
    <strong>
     示例 4:
    </strong>
   </p>
   <pre><strong>输入:</strong> 45
<strong>输出:</strong> false</pre>
   <p>
    <strong>
     进阶：
    </strong>
    <br>
    你能不使用循环或者递归来完成本题吗？
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